The present invention generally relates to the sealed closure of electrochemical batteries, and more particularly relates to the sealed closure of battery cells having a fluid consuming electrode, such as air-depolarized cell batteries, to prevent or reduce cell leakage and doming of an electrode assembly.
Electrochemical battery cells that utilize a fluid, such as oxygen or other gases, from outside the cell as an active material to produce electrical energy, such as air-depolarized battery cells, can be used to power a variety of portable electronic devices. Zinc/air cells are commonly assembled in the form of button cells which have particular utility as batteries for electronic hearing aids and other electronic devices. The zinc/air button cell typically includes a cathode can and an anode cup or cover, which together form a cell housing. Disposed within the cell housing are positive and negative electrodes (cathode and anode, respectively), a separator and an aqueous electrolyte. In an air-depolarized cell, the positive electrode is a generally spongy, porous air electrode. A gasket is disposed between the first and second housing components to seal closed the cell housing. Openings are typically provided in the cell housing to allow atmospheric air, including oxygen, to enter the positive air electrode to serve as the cathode reactant.
In a zinc/air cell, the air electrode is typically provided as an electrode mix of carbon, polytetrafluoroethylene (PTFE) resin powder, manganese dioxide, and binder impressed into a current collector screen. A microporous layer, such as a microporous PTFE film, is usually adhered to the air intake side of the air electrode to allow air to enter the air electrode mix. The air electrode with current collector screen, microporous layer, and the separator are typically assembled together as an air electrode assembly, generally in the form of a laminated sheet. The air electrode assembly is inserted into the housing such that the peripheral edges of the electrode assembly are compressed along with the gasket between the housing components when the cell housing is crimped closed. The air electrode assembly is generally flexible and spongy and includes porous materials that compress along with the gasket to provide the sealed closure of the cell housing.
The conventional insulating gasket is generally a J-shaped gasket having an outer upstanding wall, a shorter inner upstanding wall, and an interconnecting bottom base wall. The outer upstanding wall of the gasket is typically compressed between side walls of the two housing components. The base wall of the gasket is typically compressed between the bottom edge of the side wall of the anode cup or cover and the air electrode assembly which, in turn, abuts the cathode can. The inner upstanding wall of the conventional J-shaped gasket extends into the internal volume of the cell housing such that it consumes volume within the battery and does not necessarily provide an optimal sealing engagement.
Conventional electrochemical cells employing porous electrode assemblies may suffer a number of drawbacks. For example, the crimped closure of the battery housing generally causes axial forces on the can and the gasket, which forces are transmitted to the interface of the gasket and the air electrode assembly. Since the air electrode assembly is generally manufactured with high porosity, the air electrode assembly is not a rigid structural member, and thus does not always provide a robust sealed closure. During the crimped closure of the battery housing, the air electrode assembly is compressed which typically causes doming of the air electrode assembly toward the anode that is an undesirable non-flat condition. Doming of the air electrode assembly generally results in a loss of otherwise usable internal volume within the battery cell, may result in cracking of the air electrode assembly, and may lead to electrolyte leakage from the battery cell.
It is therefore desirable to provide for a battery cell that optimizes the usable internal volume of the battery housing for active materials. In particular, it is desirable to provide for an air cell that minimizes doming of the air electrode assembly. Additionally, it is desirable to provide for a battery cell that further exhibits enhanced leakproofness to ensure adequate long-term shelf life of the battery cell.